The ultrasonic diagnostic apparatus transmits an ultrasonic wave to the inside of an object by an ultrasonic probe, receives a reflection echo signal of an ultrasonic wave corresponding to the structure of a biometric tissue from the inside of the object, constructs an image such as an ultrasonic cross-sectional image or the like and displays the image for diagnosis.
It has been recently disclosed that an object is pressed by an ultrasonic probe according to a manual or mechanical method to measure an ultrasonic reception signal, a displacement of each part of a living body which is caused by the press is determined on the basis of frame data of two ultrasonic reception signals measured at different times, and an elasticity image representing elasticity of the biometric tissue is generated on the basis of the displacement data (for example, Patent Document 1).
From the viewpoint of easiness, an ultrasonic probe has been frequently used for an operation of pressing an object. That is, an ultrasonic probe is pressed against the body surface of an object to apply some degree of initial press, and an elasticity image is generated while minute pressurization and minute depressurization are repeated from this initial press state. However, according to this method, the pressurization state is greatly varied in accordance with an operator's hand operation, and thus there is a case where a proper elasticity image is not necessarily obtained.
Therefore, it is disclosed in a conventional ultrasonic diagnostic apparatus that a displacement of each site is measured on the basis of two tomographic image data measured at different times, a distribution of distortion factor of a tomographic image is determined on the basis of the displacement data, and properness of pressurization is determined on the basis of whether the distribution of distortion factor is within a proper range or not (for example, Patent Document 2).
Furthermore, it is also disclosed that a pressure sensor is provided to an object pressing face of an ultrasonic probe, and transition of measurement values of the pressure sensor is graphed and displayed together with an elasticity image (for example, Patent Document 3).    Patent Document 1: JP-A-2000-060853    Patent Document 2: JP-A-2004-351062    Patent Document 3: Publication of PCT application WO2005-120358